Singles uses the narrow sidelines—but players are not confined inside them.

The governing rule and effective version

This page applies the ITF Rules of Tennis 2026, the international rules for conventional full-court singles, including the ITF's published 2026 amendments. Under the rule book's amendment provision, changes normally take effect on 1 January following approval unless the ITF decides otherwise; this page was checked against the 2026 edition in force from 1 January 2026.

It does not treat wheelchair tennis, beach tennis or red/orange 10-and-under tennis as the same format. Those have separate ITF provisions. A tournament may also use an ITF-approved alternative procedure or an authorised trial, so its entry information and competition regulations can supplement the baseline stated here.

Do not use one rectangle for every decision

• On the serve: Rules 17 and 19 require the ball to pass over the net and hit the diagonally opposite service court. Missing that box is a service fault.
• During the rally: the baselines and singles sidelines form the correct court. A shot in a doubles alley is out; a shot beyond a service line can be good.
• For player movement: the receiver may begin inside or outside the lines on the receiver's side, and either player may run beyond a baseline or sideline. Painted boundaries decide where the ball may bounce, not where a player must keep standing.

The singles lines and service boxes

ITF Rule 1 makes a standard singles court 78 feet long by 27 feet wide. The baselines close the two ends. The inner side lines are the singles sidelines; the 36-foot doubles sidelines remain visible on many courts but do not enlarge a singles rally court.

Each serviceline is 21 feet (6.40 m) from the net. Between the net and that serviceline, the centre serviceline divides the area into two equal service courts. Court measurements are taken to the outside of the lines. Under Rule 12, touching any part of the line counts as touching the court bounded by that line.

The legal serving area is narrower than the baseline

Immediately before the service motion, ITF Rule 16 requires the server to be at rest with both feet behind—farther from the net than—the baseline and between the imaginary extensions of the centre mark and the singles sideline. Rule 18 then prohibits either foot from touching:

• the baseline or the court during the service motion;
• the imaginary extension of the centre mark; or
• the area beyond the imaginary extension of the singles sideline.

The server may make slight foot movements and may have one or both feet off the ground, but may not change position by walking or running. A breach is a foot fault, which is a service fault under Rule 19. The ITF's 2026 amendment clarified Rule 18 Case 1: standing behind the strip between the singles and doubles sidelines is allowed in doubles, but not in singles.

Right first, then alternate after every point

In every standard game, Rule 17 starts the server behind the right half of the court—commonly called the deuce side—and then alternates right, left, right, left after each point. The serve must land in the diagonally opposite service court. A tie-break also begins with a serve from the right and alternates court halves point by point, even though the identity of the server changes under the tie-break service order in Rule 5.

A first service that misses the box, is a foot fault, or otherwise breaks Rules 16–19 is a fault. Rule 20 gives a second service from the same half without delay, unless the first service was delivered from the wrong half. Two consecutive faults lose the point under Rule 24(a).

The receiver may stand anywhere on their side

ITF Rule 8 Case 1 allows the receiver to take any position inside or outside the lines on the receiver's side of the net. There is no requirement to stand behind the baseline or within the singles sidelines. A receiver may therefore move well forward, far back or beyond a sideline to deal with angle and pace.

Position does not remove the need to let the serve bounce. Returning a serve before it bounces loses the point under Rule 24(e). If the served ball strikes the receiver before bouncing, the server wins the point unless the service is a let. Under Rule 21, the server must wait until the receiver is ready, while the receiver must play to the server's reasonable pace; attempting a return is treated as readiness.

Movement outside the court is legal

Once the serve is in play, no formation rule ties either singles player to a baseline, service box or sideline. A player can approach the net, retreat behind the baseline or run outside the singles and doubles markings. What matters is whether the return lands in the correct singles court and whether the player avoids a loss-of-point act in Rule 24.

A player loses the point by touching the net, singles stick or opponent's court while the ball is in play, or by striking the ball before it has passed the net. Merely crossing the imaginary extension of the net outside the court is not itself a loss of point if the player does not touch the opponent's court. A follow-through may cross above the net only after the player struck the ball on their own side.

Singles sticks change what counts as the net

For a singles-only net, the net-post centres are 3 feet (0.914 m) outside each singles sideline. If singles is played with a wider doubles net, Rule 1 requires two singles sticks, also centred 3 feet outside the singles sidelines, to support the net at 3½ feet (1.07 m).

Rule 2 then treats the actual doubles posts and the parts of the net outside the singles sticks as permanent fixtures, not as the net for that singles match. This distinction changes edge-case rulings:

• A serve that hits a singles stick before landing is a fault, even if it then enters the correct service court (Rule 19 Case 2).
• A rally return that touches a singles stick and then lands in the correct court is good (Rule 25 Case 1).
• A rally ball that hits the doubles post or outer section of net before bouncing has hit a permanent fixture; the striker loses the point under Rule 13.
• A rally return may travel outside a net post, above or below net height, or pass under the cord between a singles stick and adjacent doubles post, if it satisfies Rule 25 and lands in the correct court.

Fault, point lost, let or play on?

• Wrong service box, foot fault or singles-stick contact on serve: service fault. A first fault leads to a second serve; a second consecutive fault loses the point.
• Serve clips the net and otherwise lands correctly: under standard Rule 22, service let; repeat that service. A previous fault is not cancelled.
• Rally ball lands in a doubles alley or beyond the baseline: striker loses the point. A relevant line touch is in.
• Player catches or volleys a ball that appears certain to go out: that player loses the point unless the contact itself is a good return. The expected landing spot is not substituted for what actually happened.
• Legal return made from outside the court: play continues. The player's location outside the lines does not make the return out.

Points stand when the serving-position error is found

ITF Rule 27 begins with the principle that previously played points stand. If a player serves from the wrong half, correct the position as soon as the error is discovered and continue from the half required by the score. A fault served before discovery still stands.

If the players are at the wrong ends, correct them as soon as the error is discovered. A fault served before that discovery does not stand. The ITF identified this Rule 27 clarification—covering the wrong-end situation during a tie-break—as a 2026 amendment. These are corrections, not permission to replay all points since the mistake began.

The standard pattern has approved alternatives

Under Rule 10, players change ends after the first, third and every later odd-numbered game of a set. They also change at the end of a set unless the set contained an even number of games; if it did, they change after the first game of the next set. A standard tie-break changes ends after every six points.

That six-point tie-break pattern is not universal. ITF Appendix VI permits an alternative change after the first point and every four points thereafter, and its five-point Short Set tie-break changes ends after the first four points. Appendix VI also permits a no-let procedure in which an otherwise good net-cord serve remains in play. The sanctioning body or event must identify the procedure being used; players should check the competition information rather than infer it from court markings.

A rally ball lands in the alley

Situation: after a legal serve, Blue hits a cross-court forehand that lands between the singles and doubles sidelines.

ITF 2026 ruling: Blue loses the point. Rule 1 makes the inner singles sideline the boundary for this match. The wider doubles line is only a marking and does not make the alley part of the correct court.

A wide serve catches the singles sideline

Situation: the serve is diagonal and a small part of the ball touches the singles sideline bordering the correct service court.

ITF 2026 ruling: the serve is in, assuming no other fault or let. Rule 12 treats a line touch as touching the court bounded by that line. The same physical singles sideline bounds both the service box and later rally court.

The server stands behind the alley

Situation: in singles, the server starts with a foot behind the portion of baseline between the singles and doubles sidelines to create a wider angle.

ITF 2026 ruling: foot fault. Rule 18 Case 1 expressly says that position is not allowed in singles. The decisive fact is the foot beyond the imaginary extension of the singles sideline, not whether it stayed behind the painted baseline.

The receiver catches an obviously long serve

Situation: the receiver is behind the baseline and catches the serve before it bounces because it is clearly travelling long.

ITF 2026 ruling: the server wins the point. Rule 24(i) and Case 7 award the point to the server when a serve hits the receiver before the bounce, unless it is a service let. The receiver should let it land.

A player runs around the net post

Situation: a sharply angled ball pulls Blue beyond the sideline. Blue runs beyond the imaginary extension of the net, strikes the ball after it has crossed to Blue's side, does not touch Red's court, and sends it outside the post into the correct court.

ITF 2026 ruling: play continues. Rule 24 Case 4 allows crossing the imaginary net extension without touching the opponent's court, and Rule 25 permits a return outside the net post when it lands in the correct court.

How to rule on a singles court question

1. Name the phase: service or rally. The service box is not the rally boundary.
2. Select the relevant lines: diagonal service court for a serve; singles sidelines and baseline after the serve.
3. Check the player restriction: server's feet, receiver's side of the net, or a Rule 24 contact—not whether the player stood inside a painted rectangle.
4. Follow the ball to its actual contact: line, ground, player, singles stick, net post or permanent fixture.
5. Apply any event procedure: standard service let and change-of-ends rules unless an approved alternative has been announced.
6. Choose the outcome: fault, second serve, point lost, let, correction or play on.

Five claims that confuse ball position with player position

• “Every marked line is live.” Doubles sidelines are out during an ordinary singles rally.
• “The service boxes stay active all point.” They limit the serve only; a later ball may land behind a serviceline.
• “The receiver must be behind the baseline.” Rule 8 permits any position on the receiver's side, inside or outside the lines.
• “A player who leaves the court loses the point.” Running outside the markings is legal; prohibited contact or an invalid return causes the loss.
• “The doubles post is always part of the singles net.” With singles sticks, Rule 2 classifies the outer net and doubles posts as permanent fixtures.

Unofficiated line-call practice is not globally universal

In an officiated ITF-rules match, Appendix VII makes the chair umpire the final authority on questions of fact. A player may call the referee for a disputed interpretation of tennis law, but not merely to re-decide whether a particular ball was in or out.

For USTA-sanctioned play in the United States, the 2026 Friend at Court adds The Code for matches without officials: players call balls on their own side, give opponents the benefit of doubt, and treat a ball that cannot confidently be called out as good (The Code §§5–8). Those USTA procedures are not part of the ITF Rules of Tennis and should not be presented as the universal self-officiating code for every country or competition.

Governing-body sources and effective version

• International Tennis Federation — Rules of Tennis 2026, Rules 1–2, 5, 8, 10–13, 16–25 and 27; Appendices VI–VIII
• International Tennis Federation — 2026 Amendments to the Rules of Tennis, Rule 18 and Rule 27 clarifications
• United States Tennis Association — Friend at Court 2026, The Code §§5–8 (U.S. unofficiated matches)

Checked on 28 August 2026 against the ITF 2026 international rule book and published 2026 amendment notice. The ITF baseline controls this page; event regulations may announce approved alternative scoring, change-of-ends or no-let procedures, and national bodies may add self-officiating procedures.